Conventionally, there have been known heat exchange ventilators that perform heat exchange between supply air and exhaust air during ventilation for cooling and heating. Particularly, in total heat exchange ventilators, which exchange both sensible heat and latent heat, a material having heat conductivity and moisture permeability is used for a partition plate, and sensible heat and latent heat are exchanged in parallel.
The total heat exchange ventilator includes a total heat exchange element for performing heat exchange. The material of the total heat exchange element is required to have gas barrier properties for preventing supply air and exhaust air from being mixed together, particularly a carbon dioxide barrier property, and heat conductivity. Particularly, a total heat exchange element that performs exchange of latent heat in parallel with exchange of sensible heat is also required to have high moisture permeability.
Therefore, for partitioning members for a total heat exchange element, attempts have been made to blend various kinds of agents having moisture permeability, such as calcium chloride and hydrophilic polymer compounds (for example, PTL 1).
In PTL 1, an aqueous solution containing a hydrophilic polymer compound is applied to a porous sheet containing hydrophilic fibers in an amount ranging from 30% by weight to 100% by weight (both inclusive). Then, the hydrophilic polymer compound is made water-insoluble at the surface, the inside or both of the porous sheet. As a result, a sheet for a total heat exchanger is formed, the sheet being a hydrophilic polymer compound-coated sheet having a porous sheet whose pores are filled up.
In such a conventional total heat exchange ventilator, dew condensation may occur in the total heat exchange element. Dew condensation occurs in the total heat exchange element in situations where there is a large difference in temperature between the interior and the outdoors as in tropical regions or cold regions, and where the humidity of either of the interior and the outdoors is higher due to ventilation at a bathroom or high-temperature and high-humidity weather.
The total heat exchange ventilator is required to have gas barrier properties as described above, and is also required to have high moisture permeability for performing latent heat exchange. For example, in PTL 1, an agent for imparting gas barrier properties has moisture permeability. However, when an aqueous solution is applied to a porous base material, and an agent contained in the aqueous solution and having gas barrier properties and moisture permeability is made water-insoluble, the partitioning member for a total heat exchange element does not have sufficient moisture permeability.
In order to compensate for the lack of moisture permeability, a method is generally employed in which an agent having moisture permeability is separately added to a material, as described in PTL 1 shown as an example. However, the agent having moisture permeability is often water-soluble, and in this case, there is a problem that the agent having moisture permeability is dissolved through dew condensation. The agent is dissolved in condensed water deposited on the surface of the partitioning member for a total heat exchange element, or the dissolved agent flows to the outside of the total heat exchange element together with condensed water. Consequently, the agent is lost from the inside of the partitioning member for a total heat exchange element.
As a result, there is a problem that moisture permeation performance of the partitioning member for a total heat exchange element is deteriorated, and latent heat exchange efficiency of the total heat exchange element is reduced. When an agent having moisture permeability is added along with an agent for securing gas barrier properties, there is a problem that the agent having moisture permeability falls out, and from holes thus created, air is leaked, so that gas barrier properties are also deteriorated.